1. Field of the Invention
The present invention relates to a liquid coating device for forming a thin film.
2. Description of the Related Art
A liquid coating device to be described below is conventionally known.
That is, in order to obtain a desired pattern of a thin film in a wafer processing step in the manufacture of semiconductor integrated circuits, a mask is formed by a thin metal film or the like having a desired pattern formed on a photosensitive resist film coated on a wafer, and the photosensitive resist is exposed and developed. In this resist coating step, coating films must be formed in same uniform thicknesses in order to form a high-quality semiconductors. A spin coater is often used for this purpose. The spin coater drops a resist from a nozzle located above a wafer by using a mechanism for supplying a predetermined amount of a resist solution and rotates a chuck which chucks the wafer by suction or the like at a high speed in a cup surrounding the chuck, thereby performing coating.
It is found that, in this coater, the film thickness of a resist coating film depends on the viscosity and the temperature of a resist solution, the temperature and the rotational speed of a wafer, and environmental factors such as ambient temperature and humidity. Therefore, these parameters are controlled by maintaining the processing conditions in the cup constant to ensure precision of the film thickness. Since, however, temperature/humidity adjusting equipment for obtaining the predetermined conditions is expensive and the parameters have mutual relationships with each other, it is difficult to set optimal conditions.